1. Field of the Invention
The invention relates to a display apparatus, more particularly to a backlighting module for a display apparatus.
2. Description of the Related Art
Backlighting modules are used to provide illuminating light to liquid crystal displays. Referring to FIG. 1, a conventional backlighting module 1 is shown to include a linear light source 11, a light guide 12, a reflector plate 13, a light diffuser 14, and a prism unit 15 including two prisms 151, 152.
The linear light source 11 is disposed adjacent to a light-incident end of the light guide 12. Light from the linear light source 11 is radiated toward the light guide 12 or is reflected by a reflector 111 toward the light guide 12. By virtue of optical elements on a lower surface of the light guide 12, and by virtue of the reflector plate 13 disposed beneath the light guide 12, which cooperate to impair the total reflection phenomenon, light incident on the light guide 12 is diffused within a certain angular range at an upper light-emergent surface of the light guide 12 toward the light diffuser 14 in a relatively uniform distribution. The light further propagates through the light diffuser 14 and the prism unit 15 for viewing angle adjustment so that the illuminating light can spread out within a certain viewing angle range of a liquid crystal display (not shown).
As the light guide 12 is the main light propagating medium in the backlighting module 1, the shape and material of the light guide 12 determine the luminosity and uniformity of the light from the light-emergent surface of the light guide 12. In order to enhance the luminosity and uniformity of the light from the light-emergent surface of the light guide 12, there are available various methods of forming light guides of different constructions, including injection molding, dot-printing, etching, cutting, sand blasting, etc.
Referring to FIG. 2, the optical elements in the light guide 12 include a plurality of elongated grooves 121 formed by cutting in the lower surface of the light guide 12. Each of the grooves 121 extends in a direction transverse to the light propagating direction of the light source 11. The light-emergent surface of the light guide 12 is also formed with a plurality of elongated grooves 122 that are transverse to the grooves 121. The total reflection effect of the light guide 12 is destroyed by virtue of two reflective surfaces 123 of each of the grooves 121, 122.
The thickness of the light guide 12 in general ranges from several hundredths of a millimeter to several millimeters. The grooves 121, 122 have a depth ranging from 15 to 100 micrometers (xcexcm, xcexc=10xe2x88x926), and a width ranging from 30 to 200 micrometers. Therefore, the depth and width of the grooves 121, 122 are very insignificant when compared to the thickness of the light guide 12.
FIG. 3 illustrates the construction of another light guide 12xe2x80x2, which is formed with a plurality of micro-reflectors 125 on a lower surface thereof. Aside from contributing to the impairment of the total reflection effect of the light guide 12xe2x80x2, the micro-reflectors 125 can also control the viewing angle distribution of the light emitted from the light-emergent surface of the light guide 12xe2x80x2. By controlling the number of the micro-reflectors 125 on the light guide 12xe2x80x2, the light emergent therefrom can be effectively modulated.
In the conventional backlighting module 1 of FIG. 1, the reflector plate 13 is required to reflect light escaping from the lower surface of the light guide 12 or 12xe2x80x2 back into the light guide 12 or 12xe2x80x2. However, the use of the reflector plate 13 increases the overall size and weight of the backlighting module 1. Besides, as a clearance, though insignificantly small, is present between the reflector plate 13 and the light guide 12 (12xe2x80x2), there will be loss of light, which will reduce the rate of reflection. Hence, there is a need in the art for an improved backlighting module.
Therefore, the main object of the present invention is to provide a backlighting module for a display apparatus, which includes a compact light guide that can reduce the overall size of the backlighting module and minimize undesirable loss of light to enhance the reflection rate.
According to the present invention, a backlighting module for a display apparatus includes:
a linear light source;
a light guide including a plate body disposed adjacent to the light source in a first direction corresponding to a light propagating direction of the light source, the plate body having first and second surfaces opposite to each other in a second direction that is transverse to the first direction, the light guide further including a dielectric layer formed on the first surface of the plate body, and a reflective layer formed on one side of the dielectric layer opposite to the first surface of the plate body, the dielectric layer having a refractive index smaller than that of the plate body, the light guide having a light incident end proximate to the light source in the first direction, wherein light from the light source enters into the light guide via the light incident end, is guided by the light guide toward the second surface of the plate body, and exits the light guide via the second surface of the plate body;
a light diffuser disposed on the second surface of the plate body to receive and diffuse light that exits from the second surface of the plate body; and
a prism assembly disposed on the light diffuser to receive and distribute light from the light diffuser.